Disposable absorbent articles such as diapers, training pants, adult incontinence products and feminine care products are well known in the art. Such disposable articles collect and retain urine and fecal material deposited thereon by the wearer.
Nonwoven fabrics made of synthetic fibers and/or natural fibers are commonly used in absorbent articles, for example, as topsheet material or as core wrap to enclose the storage layer of the absorbent core. Such nonwoven fabrics are usually hydrophobic. However, for many applications in hygiene products it is necessary to have hydrophilic nonwovens. Therefore, the nonwoven fabric has to be treated accordingly. One typical component of disposable absorbent articles is core wraps. A core wrap is typically a nonwoven material which has been rendered hydrophilic and designed to contain the storage layer and provide structural integrity when the storage layer is wet or dry. Core wraps may also be a tissue wrap.
A common method for rendering nonwoven fabrics hydrophilic or ensuring hydrophilicity is coating the surface of the nonwoven with hydrophilic surfactants. As this coating does not lead to a tight chemical bond between the nonwoven and the surfactant, coating of this type are not sufficiently durable and the surfactant can be washed off during use when the absorbent article is wetted. The decrease in liquid strike-through time is a desirable effect when the nonwoven is coated with surfactant. Liquid strike-through refers to liquid passing through the nonwoven fabric with liquid strike-through time referring to the time it takes for a certain amount of liquid to pass through the nonwoven. However, as the surfactant is washed off when coated nonwoven fabrics are exposed to the liquid, the strike-through time in successive gushes is increased. This results in performance reduction during use on diapers or other articles comprising such nonwoven fabrics. Furthermore, at the same time as liquid strike-through time decreases due to surfactant wash-off, surface tension of the liquid, which was in contact with the nonwoven fabric, is also reduced. This reduction is undesirable, because it can cause increased urine leakage in a diaper. Increasing the add-on levels of surfactants does not solve strike-through time problem. Rather, the increased add-on levels typically result in dry migration of the surfactants to other areas of the diaper, such as the barrier leg cuffs and additional surface tension reduction of the fluid to be absorbed. Thus, increased surfactant levels to render nonwovens hydrophilic can lead to multiple negative impacts when incorporated into an absorbent hygiene article.
Another common method to render a nonwoven fabric hydrophilic is by applying corona and/or plasma treatment. Plasma is an ionized form of gas that can be obtained by ionizing a gas or liquid medium. Plasmas are widely used for the treatment of organic and inorganic materials to promote adhesion between various materials. Polymers that have chemically inert surfaces with low surface energies do not allow good coatings with bondings and adhesives. Thus, these surfaces are treated to make them receptive to bonding with other substrates, coatings, adhesives and printing inks. However, corona and plasma treatments lead to low coating durability upon storage of the treated material, i.e., hydrophilicity decreases over time.
Accordingly, there is a need for a hydrophilic coating of a nonwoven, which is durable upon storage, does not migrate or transfer easily when dry or subjected to elevated temperature of storage, is not easily washed off when wetted or when fluid passes through or is in contact with the nonwoven, achieves a fast liquid strike-through time, both initially and following multiple exposures to aqueous fluids or liquids, does not lower the surface tension of the fluid to be absorbed below 55 dynes/cm, and is not easily abraded or rubbed off the surface.